The skull keys can be used as bullets for lists of items in your HTML pages. They look rather nice. I'm not sure if the other items are very useful, but since I took the time to convert them, I put them on this page anyway. I took these images from Doom using my editor and I adjusted them a bit with XV (reducing the colors to 16, changing the brightness, etc.).
Note: since Doom is copyrighted software, I am not sure about the legality issues involved in this ``derivative work''.
Doom is a trademark of Id Software, Inc.